A staff member holds a 100-carat perfect diamond in a classic emerald-cut at Sotheby's auction house in central London, February 13, 2015. The diamond is expected to fetch between $19-25 million at the auction house's Magnificent Jewels auction in New York on April 21. [Photo/Agencies]

NEW YORK - A "perfect" 100-carat diamond in a classic emerald cut is going on the auction block, where it could fetch between $19 million to $25 million.

Sotheby's will offer the white diamond on April 21 in New York. It's an internally flawless D color stone, which the auctioneer said is considered "perfect."

Sotheby's New York jewelry department head Gary Schuler likened the 100.20-carat stone's transparency "to a pool of icy water."

The stone is the only classic emerald-cut white diamond of the highest color and clarity and over 100 carats to come to auction, according to Sotheby's.

The diamond was mined in southern Africa within the last 10 years and weighed over 200 carats before it was cut and polished, the auction house said.

The owner wishes to remain anonymous.

Only five "perfect" diamonds over 100 carats have sold at auction in the last 25 years. A 118-carat oval-cut stone fetched $30.6 million at Sotheby's in 2013, setting a record for a white diamond.

A record for any diamond is $46 million for a 24.78-carat emerald-cut pink stone, set at Sotheby's in 2010. It also set a record for any jewel at auction.